these law enforcement photos show some of what they found. there's this piece of a circuit board and nails packed into the bomb that ripped through the crowd. all of the components are readily available. we were able to figure out the bomb's battery is common in power packs for remote control toys. they can be bought at almost any hobby shop. when pressure cooker bombs detonate, energy from the explosion sieve initially contained inside the cooker. then, as pressure builds, the cooker and its contents break apart with greater force. experts estimate the boston bombs shot out shrapnel at a speed of several hundred miles per hour. the bombs are being painstakingly reconstructed at the f.b.i. lab in quantico, virginia. any manufacturer numbers on the components may help lead investigators to the stores where they were sold. pressure cooker bombs are popular terrorist weapons because the parts can be bought at different stores and, scott, none of those components alone could arouse suspicion. >> pelley: elaine, thank you. also following the inves